Completeness of Earthquake Catalogues and Statistical Forecasting

Completeness of Earthquake Catalogues and Statistical Forecasting

byAndrzej Kijko

Council for GeosciencePretoria, South Africa

International Conference on “Global Change”Islamabad, 13-17 November 2006

OUTLINE

• Incompleteness of catalogues

• Uncertainties (location, magnitudes and origin times)

• Inadequate model of seismicity

• Seismogenic zones

• Maximum earthquake magnitude mmax

Surprise, Surprise!

APPROACH 1: Parametric Procedure

(Cornell, 1968)

SITE SITE

PARAMETERS•activity rate λ•b-value•maximum magnitude mmax

Advantages:

• Can account for seismic gaps, non-stationary seismicity, faults etc.

Disadvantages:

• Specification of seismogenic zones• Requires knowledge of seismic hazard

parameters (e.g. activity rate, b-value, mmax) for each zone

APPROACH 2 Non-parametric “Historic” Procedure

(Veneziano, et al., 1984)

Advantages

• No division into seismic zones needed• Seismic parameters no required

Disadvantages

• Unreliability at low probabilities, or at the areas with low seismicity

• The procedure does not take into account incompleteness and uncertainty of earthquake catalogues

ALTERNATIVE Combination of both

The ‘Parametric - Historic’ procedure• Assessment of basic hazard parameters (e.g.

seismic activity rate, b-value, mmax) for the area in the vicinity of the particular site

• Assessment of the distribution function for amplitude of ground motion for a specified site.

• If the procedure is applied to all grid points a seismic hazard map can be obtained

Epicentre500 km

PARAMETRIC-HISTORIC PROCEDURE

INCOMPLETENESS AND UNCERTAINTIES OF SEISMIC CATALOGUES

Kijko, A. and Sellevoll, M.A. 1992. Estimation of earthquake hazard parameters from incomplete data files. Part II. Incorporation of magnitude heterogeneity. BSSA, 82(1),

120-134.

MAGNITUDE DISTRIBUTION

Magnitude, m

log

n

log n = a - bm

APPLICATION TO THE GUTENBERG-RICHTER MAGNITUDE DISTRIBUTION

.,)](exp[1)](exp[1

,1

0)(

max

maxmin

min,

minmax

min

mmformmmfor

mmfor

mmmmmFM

>≤≤

<

⎪⎪⎩

⎪⎪⎨

⎧

−−−−−−

=ββ

)10ln(bwhere =βHow???

PGA DISTRIBUTION

• Please note:

2/ cβγ =

ln (PGA), x

lnn

ln n = α - γx

,lnln 4321 rcrcmcca ⋅+⋅+⋅+=2/ cβγ = where

APPLICATIONSSeismic Hazard Map of Sub-Saharan Africa

10% Probability of exceedance of PGA in 50 years

SOUTH AFRICASeismological Monitoring Network

$

$

$

$

$

$

$

$

$

$

$

$

$

$$

$

$

$

$

$

$

34° 34°

32° 32°

30° 30°

28° 28°

26° 26°

24° 24°

22° 22°

14°

14°

16°

16°

18°

18°

20°

20°

22°

22°

24°

24°

26°

26°

28°

28°

30°

30°

32°

32°

34°

34°

MSNA

MOPALEP

BFTSLRKSR

SWZNWL

POGPRYS

SEK

HVD KSD

GRM

SOE

PKA

CVNA

ELIM

CER

UPI

KOMG

Seismological station$

LEGEND

100 0 100 200 Kilometers

Gold and Diamonds

Gold pouringKimberley Big Hole

Mine Shaft

Diamonds

Krugerrand

Star of Africa

Magnitude = 5.2 at Welkom 1976

Stilfontein, 9 March 2005, ML = 5.3

Tulbagh, 29 September 1969, ML = 6.3

Seismic Hazard Map of South Africa

Maximum Possible Earthquake magnitude in Johannesburg/Pretoria?

Definition of mmax

• The maximum regional magnitude, mmax, is the upper limit of magnitude for a given region

Δ+= obsmm maxmaxˆ

The Generic Formula for Estimation of the Maximum Regional Magnitude, mmax

[ ]∫+=max

min

d)(ˆ maxmax

m

m

nM

obs mmFmm

THREE REAL LIFE CASES

1. Earthquake Magnitudes are Distributed according to the Gutenberg-Richter relation

2. Earthquake Magnitude Distribution deviates largely from the Gutenberg-Richter relation

3. No specific model for The Earthquake Magnitude Distribution is assumed

CASE 1: Earthquake Magnitudes are Distributed according to the Gutenberg-Richter relation

Magnitude, m

log

n

log n = a - bm

.,)](exp[1)](exp[1

,1

0)(

max

maxmin

min,

minmax

min

mmformmmfor

mmfor

mmmmmFM

>≤≤

<

⎪⎪⎩

⎪⎪⎨

⎧

−−−−−−

=ββ

where β = b ln 10

Case 1

( ) ( )( ) ( )nm

nnEnEmm obs −+

−−

+= expexp

ˆ min2

1121maxmax β

)(1 •E

)](exp[ minmax12 mmnn obs −−= β

where

And denotes an exponential integral function

)](exp[1{ minmax1 mm

nn obs −−−=

β

Case 2: The Earthquake

Magnitude Distribution

deviates largely from the

Gutenberg-Richter relation

Case 2: The Earthquake Magnitude Distribution deviates largely from the

Gutenberg-Richter relationEarthquake magnitude distribution follow the Gutenberg-

Richter relation with some uncertainty in the value

β

( )⎪⎩

⎪⎨

⎧

>≤≤

<−+−=

max

maxmin

min

min) },)]/([1{1

0

mmformmmfor

mmformmppCmF q

M β

β

Case 2

][ ),/1(),/1()]1/(exp[ˆ/1

maxmax δδβ

δ qrqrnrmm qqqq

obs −Γ−−Γ−

+=

βσ)(•Γ

β

where

,minmax mmp

pr−+

=,βδ nC= ,11

qrC

−=β

,)/( 2βσβ=p 2)/( βσβ=q

is the incomplete delta functionand is the known standard deviation of

This formula can be used where there exists temporal trends, cycles, short-term oscillations and pure random fluctuations

in the seismic process

What does one do when the emperical distribution of earthquake magnitude is of the following form…

Case 3: No specific model for The Earthquake Magnitude Distribution is

assumed• A non-parametric estimator of an unknown

PDFfor sample data mi , i=1,…n,:

• Where h is a smoothing factor and is a kernel function

∑=

⎟⎠⎞

⎜⎝⎛ −

=n

i

iM h

mmKnh

mf1

1)(ˆ

)(•K

Case 3: Continued…

Case 3: Continued…

• From the functional form of the kernel and from the fact that the data comes from a finite interval, one can derive the estimator of the CDF of earthquake magnitude:

• Where denotes the standard Gaussian CDF

⎪⎪⎪⎪

⎭

⎪⎪⎪⎪

⎬

⎫

⎪⎪⎪⎪

⎩

⎪⎪⎪⎪

⎨

⎧

>

≤≤

<

⎟⎠⎞

⎜⎝⎛ −

−⎟⎠⎞

⎜⎝⎛ −

⎟⎠⎞

⎜⎝⎛ −

−⎟⎠⎞

⎜⎝⎛ −

=

∑

∑

=

=

max

maxmin

min,

1

minmax

1

min

,

,1

,0

)(ˆ

mmfor

mmmfor

mmfor

hmm

hmm

hmm

hmm

mF n

i

ii

n

i

ii

M

φφ

φφ

)(•φ

Application 1: Southern California

CASE Assumptions mmax ± SD

1

2

3

Gutenberg-Richter 8.32 ±0.43

Gutenberg-Richter+ Uncertainty in b-value

8.31 ±0.42

No model for distribution is assumed (Non-parametric procedure)

8.34 ±0.45

Field et al. 1999 7.99

Fitting of Observations using the Non-Parametric Procedure

Application 2: New Madrid Zone

5 5.5 6 6.5 7 7.5 8 8.5 910

1

102

103

104

105

106

Magnitude [mb]

Mea

n R

etur

n P

erio

d [Y

EAR

S]

New Madrid Seismic Zone

Prehistoric events excludedPrehistoric events included

mmax = 7.9

mmax = 8.7

CONCLUSIONS

• It is possible to develop a lot of useful tools which is capable of taking even the most diverse behaviour of seismic activity into account

• A lot needs to be done to improve it.

THE END

THANK YOU